Biology Reference
In-Depth Information
The Fe- and Mn-SODs show high homology in their primary and three-dimensional structures.
The crystal structures of Fe-SOD of
T
.
elongatus
BP-1 and Mn-SOD of
Anabaena
sp. strain PCC 7120
in monomeric and dimeric states with the catalytically active amino acid residues are depicted in
Fig. 14. The number of amino acid residues and molecular weights differ in both cases. Cyanobacterial
Fe-SODs possess 199-229 amino acid residues with a molecular weight ranging 21-25 kDa. The
Mn-SODs have 200-316 amino acid residues with a molecular weight ranging 22-34 kDa. Both
Fe- and Mn-SODs typically exist as homodimers or homotetramers. Topologically, the presence
of α-N-terminal and a α/β-C-terminal domain is a characteristic feature of Fe- and Mn-SODs. In
cyanobacteria, an intervening highly conserved sequence motif [Asp-Val-Trp-Glu-His-Ala-Tyr-
Tyr-(Asp282-Tyr289)] is present that extends between the second α-helix and the fi rst β-sheet of the
C-terminal domain of both the SODs. The active site contains a single Fe-ion and the highly conserved
Asp282 and His286 constitute the metal-binding amino acid residues (Fig. 15). The other amino
acids of this highly conserved region are Glu285 and Tyr289 that form a dimer surface spanning
the interface and bridging the active sites between the opposite halves of each subunit (Priya
et al
.,
2007). The Fe- and Mn-SODs differ in three important aspects. The fi rst one pertains to the metal
Figure 14
: Structure of Fe and MnSOD. Structures are visualized using WebLab ViewerLite 4.2 software. Catalytically essential
aspartate or histidine residues are represented in ball and stick mode binding the active metal (yellow) is shown to identify
the location of the active site. Protein database codes are given in parentheses: (i) FeSOD (PDB 1gv3); (ii) MnSOD (PDB
1my6). (A) FeSOD of
Thermosynechococcus elongatus
BP-1 dimers are distinguished by colour (violet and slate), and structures
are represented with the active site (yellow) of subunit. (B) Monomeric subunit of FeSOD represents an N-terminal (green)
and a C-terminal (red). Similarly (C) represents dimer structure of
Anabaena
sp. MnSOD in pink and green with active site
highlighted in yellow. (D) Monomeric MnSOD showing the N-terminal residues in blue and C-terminal in pink with metal
binding ligands. The transmembrane hydrophobic pocket specifi c for MnSOD is highlighted in red (D). Picture with the
kind permission of B. Priya, National Facility for Marine Cyanobacteria (Sponsored by Department of Biotechnology, Govt.
of India), Department of Marine Biotechnology, School of Marine Sciences, Bharathidasan University, Tiruchirappalli, Tamil
Nadu, India. [Priya
et al
. (2007)
BMC Genomics
8:
435. doi:10.1186/1471-2164-8-435].
Color image of this figure appears in the color plate section at the end of the topic.
